Brittany Nelson-Cheesman
Univeristy of Wisconsin
Materials Science and Engineering

Spontaneous Infiltration of Porous SiC Preform by Al-Si Alloys

Introduction

Ceramic Matrix Composites, composites consisting of a porous ceramic matrix infiltrated with molten metal or alloy, are becoming a much sought after material in many different industries today. This is due largely to the fact that such a composite incorporates both the beneficial properties of a ceramic, such as low thermal expansion coefficient, high thermal conductivity, high abrasion/wear resistance, and low density; while improving other, usually less flattering ceramic properties, such as fracture toughness, ductility or conductivity, due to the reinforcement from the metal. However, most metals do not wet (a measure of a liquid's affinity for a solid) ceramics well, and must be processed under certain conditions to do so. In this project, the Al-Si alloy system was observed as to how it reacted with Reaction Bonded SiC under different processing conditions.

Project Objectives

  • Observe porosity of Reaction Bonded SiC perform
  • Observe change in contact angle due to change in processing conditions
  • Successfully infiltrate Al-Si alloy into porous SiC preform
  • Find optimal conditions for infiltration of Al alloys into porous SiC perform

Experimental Approach

Heating furnace beyond the alloy melting temperature and then holding at an elevated temperature for a specified amount of time to allow for infilitration of molten alloy into preform. Varying such parameters as pressure of processing (from vacuum to 1 atm), temperature of processing (from 1000oC to 1300 oC, soak time of processing (from 20 min to 1 hr), preparation of SiC perform (etched or non-etched) and silicon content in Al-Si Alloy (0 - 30wt%Si.) After cooling, samples were cut in half with a diamond blade, so that a rough estimate of the contact angle and the infiltration depth could be observed from the cross section. If infiltration appeared, the samples were polished and viewed with digital microscopy.

Research Findings


Pure Al at 1000 oC
30wt%Si-Al Alloy at 1300 oC on etched SiC.